Method of preparing carbon resistance stacks



Jan. 31, 1933. s, PETERS 1,895,519

METHOD OF PREPARING CARBON RESISTANCE STACKS Filed June 6, 1929 Fig.

Fig. 5.

Invmon:

Orville 5. Peters,

Patented Jan. 31, 1933 UNITED STATES PATENT OFFICE ORVILLE S. PETERS, OF CHEVY CHASE, MARYLAND v METHOD OF PREPARING CARBON RESISTANCE STACKS Application ,filed June 6, 1929. Serial No. 368,885.

My invention relates to the preparation of carbon stacks employed as resistance elements in various forms of electrical apparatus,

measuring instruments, electric telemetricdevices, etc., one instance of a structure of the latter type being illustrated and claimed in my Patent No. 1,528,627, March 3, 1925.

The object of my invention is to standardize the piles 0r stacks of carbon disks eml0 ployed with instruments of this character whereby the pressure resistance characteristics of each of a plurality of stacks arranged in series or in multiple shall be identical and constantly reproducible so that like changes of pressure shall produce like changes of resistance in the several stacks.

In the construction and development of electric telemetric measuring instruments of the type disclosed in my patent above referred to, employing a pair of carbon stacks arranged in series, it is essential that the pressure resistance characteristics of these stacks shall be identical and constantly reproducible.

The deflections of an instrument such as 2 indicated at 32 in my patent above referred to depend upon the current, indicated by the ammeter associated therewith which in turn indicates the changes of resistance in the carbon stacks arranged in series. In or- 80 der that these deflections may be alike from time to time under like conditions of measurement, it is necessary that the changes of resistance of each of the carbon stacks be the same for like conditions, and in order that 85 I may produce stacks fulfilling these requirements, have developed an improved method of reparing the carbon rings or disks and of inning the stacks.

In the employment of pairs of carbon 4 stacks in the relation indicated in my patent ,fiabove referred to, it is essential that each stack possess the same pressure resistance characteristics. For instruments using single stacks it is also important that each stack 4 possess the same pressure resistance curve, because in cases where single stacks arebuilt into separate instruments the similarity of the stacks reduces the labor otherwise necessary to adjust the several instruments to give 5 like readings under like conditions.

In the commercial production of carbon stacks it has proved difficult to coordinate stacks of carbon disks made in different batches and to" insure that the pressure resistance characteristics of one group of carbon disks arranged in a stack will be identical with the pressure resistancecharacteristics ofanother stack having the same number of carbon disks. I have discovered that, in order to produce stacks having identical pressure resistance characteristics, not only must the stacks contain the same number of disks but if the stacks having the same number of disks can be made to have the same resistance under one pressure, similar variations in pressure will produce similar resistances in the difierent stacks and the parabolas indicating their pressure resistance changes will be identical. The object of my invention is to reproduce in pairs, or other convenient quantities, stacks or piles of carbon disks each having the same number of disks and in which the pressure resistance characteristics will be the same and constantly reproducible.

In the accompanying drawing I have indicated diagrammatically carbon rings or disks made in accordance with my invention, in which:

Figure 1 indicates a pile of carbon disks; Fig. 2 an enlarged plan view of a single disk, and

Fig. 3 an elevation of Fig. 2.

The carbon rings or disks indicated at 10 are usually mounted in stack form; Fig. 1, illustrating a verticai stack. and disposed between metal mcmbcrs 11 to which conducting wires 12 may be connected; such members 11 being separated from metal plates 13 forming part of supporting means for the carbon stacks, by insulating disks 14.

These carbon rings or disks in completely finished form are approximately .018 to .02 inches in thickness. and the piles or stacks employed as pressure resistance elements may comprise fifty (50) of these rings or disks.

The carbon disks making up the siacksemployed in devices of the character set forth in my patent referred to may be produced from various materials such, for example, as powdered coke, graphite, etc., which may be carbonized under heat and pressure and in practice I have used a number of easily available materials, the particulars of which it seems unnecessary to note. In preparing the disks employed in these carbon stacks, I find that the resistance of the disks of successive batches will vary in relatively wide ranges and with a view of preparing stacks having a known resistance of a suitable quantity, I may proceed as follows.

The material employed in the manufacture of these carbon disks is initially granular or pulverulent, and is compressed into substantially the final form by suitable means.

To insure that the respective disks shall have the same amouht of---material, compressed to theisame degree, and of thesame thickness, such compressing means are preferably arranged so that;excessiifateria.l m ay flow through apertures of the dies to insure that the salient features mentioned can be uniform, insofar as the preliminary-steps are rin , these carbon disks are concerned,,in the production of'successive or disks of such material subsequently car nized.

In the use of the. material from which roduced, a binder may be employed and the rst step after-compression' 1s a baking operation which setssuch binder (when used) and insures coherence of the compressed particles of the material employed injthe-subsfequent heat treatment.

This baking operation may be carried on at a temperature of about 130 C. for a period of approximately three hour From the baking chamber the rings or disks are introduced into a carbonizing furmace and are slowly brought to a red heat at a temperature of about 650 C., within'a period of approximately forty-eight hours. The heat is then shut off and the carbon rings or disks are allowed to cool slowlyin the container in which they have been car bonized. During the carbonizing treatment, the disks are embedded in lamp black for the purpose of consuming any oxygen in the material employed or in the chamber in which 'carbonization takes place, and to insure a complete exclusion of air, the chamber or container receiving the disks for carboniza tlon is embedded in a body of lime or similar material.

This method of manufacture produces batches of these carbon disks at each operation, and the usual practice is to carbonize In my the same quantity at each operation.

have carbonized batches of one practice I thousand disks. Followingr carhonization, the disks are ground on opposite faces 'to insure uniformity of the surface and that such faces shall be parallel and fiat.

' grinding operation, that theaimular disks I do not possess identical pressure resistance characteristics.

In the'development'bf the carbon stacks as I have carried the same into effect, it has been desirable, for instance, to produce stacks, say of50 discs whose total resistance may be approximately eighty (80) ohms at a total'pressure of twenty (20) pounds. I

have found that the resistance of therespective stacks of carbon disks at this pressure may vary between 50 and 150 ohms; 1

Forexample, although it is possible to pro duce a batch of disks, fifty 'of which will give a resistance of 1200 to 1350 ohms; another batch of which any fifty (50) disks will give a resistance of between 1400 and 1450 ohms and so on, it is impossible to producea batch fromwhich two stacks of fifty (50) disks may be picked atrandom' which will give the same tota l resistance at'the same pressure, say 1220 ohms.

- It has. heretofore been-the practiceto in crease or decrease the-number of disks'in the stack to make the resistances of two stacks. under given pressure the fsame'. lhe' result-of the practice of'this method was to, produce stacks in nojtw o of which a'change in pressure would produce identical changes in resistance, i. e., in no two of which would" the pressure resistance para'bolas be identical In order to utilize my discovery and pro duce standardized stacks .in each of which the resistance will be equal at all of a pluralit' of'prssures, I have found that by care ully assorting disks from respective batches I can (levelop\st andardized stacks containing equal-number of discs, all stacks possessing identical and constantly repro-' ducible' pressure resistance characteristics. I

The basis for this method/of producing standardized stacks from different batches havin difierent ressurc resistance characteristics is'fou'nd in the facttha't resistance characteristic of a plurality'of, carbon disks is a parabola of the form where w relates't o pressure, gfto resistt e' p essu e permits pears that the individual pressure resistance characteristics of a plurality of stacks of the same material, but prepared at random, form a family of curves.

The process of standardizing the stacks then consists in selecting some particular curve, for instance, one in which a standard stack shows 80 ohms at 20 ounds total ressure, and selecting disks rom batches aving greater and less resistance at this pressure in sufficient number and ratio so that when stacked up the average resistance at the given pressure shall be the required value. In practice, this 0 eration is readily and speedily accomplishe by first estimating the numbers of disks to be selected from the different batches, and then, by repeated tests and replacements as required to approach the required value near enough for engineering purposes.

A stack so prepared, being composed of elements having the same fundamental characteristics in different degree, presents an average charcateristic which can be repeated in an indefinite number of stacks if the elements are properly selected, although it is not necessary that the elements be the same in every case. It is necessary only that the average be the same in every case.

For example, after pre aring the first stack so as to obtain the desired resistance at a given pressure, an indefinite number of stacks maybe prepared, each having the same resistance as the first stack at all pressures, by havin the same numberof disks in each stack as is in the original stack and substituting disks of different resistances until at any one pressure common to both the original stack and thestack beingformed the resistance is the same and, t s result being attained, the resistances of the stacks will be the "same at all pressures,

Thus the preparation of stacks of disks as regards standardization of their pressure resistance characteristics is removed from the chance of random selection and placed upon a plhysico-mathematical basis which stacks to exact specifications.

I claim 1. The method of forming a plurality of resistance stacks, which comprises forming one stack having the desired resistance characteristics of a plurality of carbon discs of non-unform resistance characteristics, and formin succeedin stacks of the same number of iscs as the rst stack but selectingthe discs so that the total resistance of each succeeding stack is the same as that of the first stack at any common ressure.

2. The method of orming a plurality of resistance stacks having identical pressure resistance parabolas, which comprises selecting and assembling a plurality of resist ance discs having non-uniform resistance formation of large numbers of characteristics in sufiicient number to give the desired total resistance of the stack at a given pressure and forming subsequent stacks by assembling the same number of discs into stacks but selecting said discs to impose the same resistance as is imposed by the first stack at any common pressure.

3. The method of forming resistance stacks composed of a plurality of disks having non-uniform pressure resistance characteristics, which comprises selecting and assembling suflicient dlsks to produce a stack having the pressure resistance characteristics desired, and forming each subsequent stack of the same number of disks as is contained in the first stack but selectin the disks so that the sum of'the resistances 1s ual to the resistance ofl'ered b the first stac under a similar pressure, w ereby the resistance offered by said subs uent stacks will be the same as that of the rst stack at every common pressure.

4. The method of forming a plurality o resistance stacks having a common pressure resistance parabola from disks having nonuniform pressure resistance characteristics, which comprises selecting and asembling a plurality of disks to form a stack havin the desired resistance at a iven pressure; forming all subsequent staclrs by assembling the same number of disks as in the first stack; and var ing the resistivity of the stack to approac the desired form by substituting disks of greater or lesser resistances while maintaining constant the number of disks in the stack.

In witness whereof I have signed this specification.

ORVILLE S. PETERS. 

